So set up a drawing:
Next, x represents the width of the house. I would use the pythagorean theorem. \(\ \huge (210)^2 + (x)^2 = (-\frac{7}{2})^2 \). By the way, the Pythagorean Theorem is \(\ \huge a^2 + b^2 = c^2 \). Then, I would solve for \(\ \huge x \).